The group says it has carried out several similar attacks in the past, among them the recent double explosion at a weapons plant.
Mohammed Sulman, a senior police official in the area, said many people were trapped under the debris of two damaged buildings in a nearby market.
Television footage showed obliterated vehicles and pieces of the checkpoint scattered across a large area.
At Lady Reading Hospital in Peshawar, the provincial capital of North West Froniter Province, officials said about 30 wounded people had come for treatment on Saturday.
"They have got multiple wounds," physician Mohammad Idrees said. "Some of them have their arms and legs broken, and others have got head injuries.
"We have declared an emergency here."
The explosion came as members of parliament and the country's four provincial assemblies were voting for a new president to replace Pervez Musharraf, who resigned last month.
Asif Ali Zardari, the Pakistan People's Party presidential nominee, widely expected to win the vote in Saturday's vote. He has vowed to be tough on militancy.
Pockets of Pakistan's northwest are considered strongholds of pro-Taliban fighters.
In recent weeks, the Pakistani Taliban has claimed responsibility for a string of suicide bombings they have called revenge for military offensives in the region, which borders Afghanistan.
The US has pushed Pakistan to crack down on fighters in the area.
A recent US-led ground assault on a Pakistani tribal region near the border, however, prompted protests from the government.